Let's roll up our sleeves and solve this. We have 503 and we're going to multiply it by 102, essentially adding 503 to itself 102 times.
Step 1: 0 + 503 = 503
Step 2: 503 + 503 = 1006
Step 3: 1006 + 503 = 1509
Step 4: 1509 + 503 = 2012
Step 5: 2012 + 503 = 2515
Step 6: 2515 + 503 = 3018
Step 7: 3018 + 503 = 3521
Step 8: 3521 + 503 = 4024
Step 9: 4024 + 503 = 4527
Step 10: 4527 + 503 = 5030
Step 11: 5030 + 503 = 5533
Step 12: 5533 + 503 = 6036
Step 13: 6036 + 503 = 6539
Step 14: 6539 + 503 = 7042
Step 15: 7042 + 503 = 7545
Step 16: 7545 + 503 = 8048
Step 17: 8048 + 503 = 8551
Step 18: 8551 + 503 = 9054
Step 19: 9054 + 503 = 9557
Step 20: 9557 + 503 = 10060
Step 21: 10060 + 503 = 10563
Step 22: 10563 + 503 = 11066
Step 23: 11066 + 503 = 11569
Step 24: 11569 + 503 = 12072
Step 25: 12072 + 503 = 12575
Step 26: 12575 + 503 = 13078
Step 27: 13078 + 503 = 13581
Step 28: 13581 + 503 = 14084
Step 29: 14084 + 503 = 14587
Step 30: 14587 + 503 = 15090
Step 31: 15090 + 503 = 15593
Step 32: 15593 + 503 = 16096
Step 33: 16096 + 503 = 16599
Step 34: 16599 + 503 = 17102
Step 35: 17102 + 503 = 17605
Step 36: 17605 + 503 = 18108
Step 37: 18108 + 503 = 18611
Step 38: 18611 + 503 = 19114
Step 39: 19114 + 503 = 19617
Step 40: 19617 + 503 = 20120
Step 41: 20120 + 503 = 20623
Step 42: 20623 + 503 = 21126
Step 43: 21126 + 503 = 21629
Step 44: 21629 + 503 = 22132
Step 45: 22132 + 503 = 22635
Step 46: 22635 + 503 = 23138
Step 47: 23138 + 503 = 23641
Step 48: 23641 + 503 = 24144
Step 49: 24144 + 503 = 24647
Step 50: 24647 + 503 = 25150
Step 51: 25150 + 503 = 25653
Step 52: 25653 + 503 = 26156
Step 53: 26156 + 503 = 26659
Step 54: 26659 + 503 = 27162
Step 55: 27162 + 503 = 27665
Step 56: 27665 + 503 = 28168
Step 57: 28168 + 503 = 28671
Step 58: 28671 + 503 = 29174
Step 59: 29174 + 503 = 29677
Step 60: 29677 + 503 = 30180
Step 61: 30180 + 503 = 30683
Step 62: 30683 + 503 = 31186
Step 63: 31186 + 503 = 31689
Step 64: 31689 + 503 = 32192
Step 65: 32192 + 503 = 32695
Step 66: 32695 + 503 = 33198
Step 67: 33198 + 503 = 33701
Step 68: 33701 + 503 = 34204
Step 69: 34204 + 503 = 34707
Step 70: 34707 + 503 = 35210
Step 71: 35210 + 503 = 35713
Step 72: 35713 + 503 = 36216
Step 73: 36216 + 503 = 36719
Step 74: 36719 + 503 = 37222
Step 75: 37222 + 503 = 37725
Step 76: 37725 + 503 = 38228
Step 77: 38228 + 503 = 38731
Step 78: 38731 + 503 = 39234
Step 79: 39234 + 503 = 39737
Step 80: 39737 + 503 = 40240
Step 81: 40240 + 503 = 40743
Step 82: 40743 + 503 = 41246
Step 83: 41246 + 503 = 41749
Step 84: 41749 + 503 = 42252
Step 85: 42252 + 503 = 42755
Step 86: 42755 + 503 = 43258
Step 87: 43258 + 503 = 43761
Step 88: 43761 + 503 = 44264
Step 89: 44264 + 503 = 44767
Step 90: 44767 + 503 = 45270
Step 91: 45270 + 503 = 45773
Step 92: 45773 + 503 = 46276
Step 93: 46276 + 503 = 46779
Step 94: 46779 + 503 = 47282
Step 95: 47282 + 503 = 47785
Step 96: 47785 + 503 = 48288
Step 97: 48288 + 503 = 48791
Step 98: 48791 + 503 = 49294
Step 99: 49294 + 503 = 49797
Step 100: 49797 + 503 = 50300
Step 101: 50300 + 503 = 50803
Step 102: 50803 + 503 = 51306

So, 503*102 = 51306